The present invention relates to an actuating device for displacing a control device. Such a control device is e.g. a valve, a gate valve, a so-called blow-out preventer or some other control mechanism used in the field of oil and natural gas production, in particular in the maritime sphere. Such a control device is provided with a suitable actuating element which is adapted to be displaced by the actuating device so as to displace e.g. a valve as a control device to the open or to the closed position.
The actuating device comprises at least a motor-gear unit and a thread drive, in particular roller bearing spindle drive, which is operable by said motor-gear unit and which comprises a threaded spindle and a screw nut. The screw nut is normally supported in the actuating device such that it is rotatable, but not displaceable in the axial direction, whereas the threaded spindle is adapted to be axially displaced by rotating the screw nut, so as to displace the control device between an advanced position and a retracted position. In addition, the actuating device comprises a position holding means holding the attained position of the threaded spindle. This position holding means especially prevents the threaded spindle from returning automatically from the attained position.
EP 1 281 111 B1 discloses such an actuating device and a method of operating said actuating device. The position holding means is defined by a loop spring or volute spring which is arranged between a connection sleeve and an annular shoulder of the actuating device. This loop spring allows, on the one hand, a rotation of the connection sleeve in the advance direction of the rotary spindle, whereas, on the other hand, a return torque applied to the rotary spindle by the control device is taken up by the volute spring. The threaded spindle can only be retracted from the attained position, when the respective loop spring has been released.
Furthermore, an additional volute spring is normally used, which is compressed while the threaded spindle is being displaced to the position to be attained and which will reset the control device to a safe position, especially if the power supply to the motor-gear unit should fail, such a safe position being, in the case of a valve, e.g. a closed position.
On the whole, the known actuating device is well adapted to be used, especially below the water surface, for control devices of the type in question, such as valves, flow control valves or the like, and, if respective components, such as the motor-gear unit, should fail, it also allows fault-proof operation.